In the world of philanthropy and tax-deductible charitable giving, the explosion of donor-advised funds has touched off intense debate. Now, there is evidence that the DAF boom is being further fueled by hedge fund foundation money.

Foundations established by billionaire hedge fund managers Stephen Mandel and Israel Englander, together with foundations set up by Renaissance Technologies CEO Peter Brown and former hedge fund manager Robert Karr, were among the top five foundations that gave the most to big DAFs between 2014 and 2016, The Chronicle of Philanthropy found.

DAFs are vehicles where individuals can deposit, or park, their charitable cash while receiving the corresponding tax deduction until they identify a specific cause to fund. Proponents claim DAFs promote charitable giving because they remove the tax-year time pressure of figuring out exactly where the funds will ultimately go. They can also mitigate time pressure for foundations, which are obligated to distribute 5% of their assets each year for charitable purposes.

But DAFs are controversial because they are opaque. Foundations and individuals can shield grants from public view by making them through a DAF, which can contribute gifts anonymously. Democratic Senator Sheldon Whitehouse has called this “identity laundering.”

Izzy Englander, the billionaire founder of hedge fund Millennium Management, is known on Wall Street for avoiding publicity. The Chronicle of Philanthropy linked the under-the-radar 138 Foundation to Englander through a New York State certificate of incorporation.

138 Foundation received $154 million from a limited liability corporation controlled by Englander and contributed $100 million to DAFs between fiscal 2014 and 2016. Billionaire Steve Mandel’s Zoom Foundation also gave about $100 million to DAFs between 2014 and 2016. The Quetzal Trust, which is funded by Renaissance’s Brown, contributed $41 million to a DAF and the foundation of Robert Karr, who shut down his Joho Capital hedge fund a few years ago, contributed $38 million to DAFs.